What is the biggest threat to underwater life?

Tom - This is a very hard question to answer because those three problems, which are just some of the problems that living creatures face in the oceans, they really depend on what kind of animal you are, where you live, and what kind of timescale you measure it over. So you can overfish a reef and then stop fishing and then that reef can be recolonised often and within a few generations you can have a vibrant community. But it can be absolutely devastated if you really overfish all the places around nearby or if you fish things to extinction, they can't bounce back from that. Plastic pollution - I've seen the impact of whales getting tangled and dying because they're caught in ghost nets and other plastic pollution. We can measure that very well. But what we can't measure, or not really understand yet, is what happens to all the microplastics that are so ubiquitous.

I think recently we found they could cross the blood brain barrier? These are going to be generational effects and they could be things that we can't measure or can't fix until they're too late. And with climate change, there are already winners and losers in the oceans emerging. In whales, for instance, in Antarctica, as the ice melts, that's making some places available to whales that couldn't really navigate around ice or weren't really comfortable. So their populations are going up, but other whales are losing the crill that they've fed off, or they're less comfortable in those warmer waters and they're having to move. So that's a really bad answer to the question because I don't know, but all of these things are so interlinked and they depend on where you are and the scale of the problem where you are.